A 4.00-kg box sits atop a 10.0-kg box on a horizontal table. The coefficient of kinetic friction between the two boxes and between the lower box and the table is 0.600, while the coefficient of static friction between these same surfaces is 0.800. A horizontal pull to the right is exerted on the lower box, as shown in the figure, and the boxes move together. What is the friction force on the UPPER box? 
Definitions:
Efficiency
The extent to which resources are used in the most productive way possible to produce desired goods and services while minimizing waste or inefficiency.
Economic Pie
A metaphorical representation of the total wealth or economic resources available for allocation or distribution within an economy.
Average Cost
The total cost of production divided by the quantity produced, indicating the cost per unit of output.
Unlimited Resources
A theoretical scenario where resources are abundant and not finite, eliminating scarcity and its associated challenges.
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